2 Answers
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In terms of making sure your camera is safe - make sure that when choosing a bag, the camera and any other components you're likely to be carrying fit snugly inside. It's better if it's a tiny bit too tight to begin with, as padding compacts over time.

If your bag is made of fabric and you're outdoors a lot, consider going to a hiking/outdoors store and getting some waterproofing spray (check what types of fabric it'll work on first!) for the outside of your bag.

I'll also second vacuuming the inside, and add that it's often a good idea to tie a piece of stockings or similar fabric over the end, so that if the seams aren't as good as they should be or your vacuum is too strong, nothing comes apart and gets sucked in. Exercise caution if using a powerful vacuum cleaner.

Little practical things: try not to leave the bag open in a place where it'll gather dust or grit or worse inside it; be careful what surfaces you put it down on; and check the strap and attachments once in a while, esp. if it's an older bag, to make sure nothing'll give way and send the bag (and its precious contents) into freefall at an inopportune time.

Ensure that the padding is still in good condition and positioned to stop the camera / lens from moving around to much. To clean the outside of the bag a soft brush and some water should do the trick. As for the inside depending on the material type, a damp cloth or a can of compressed air should clear out any dust. If you have a small attachment you could also vacuum the bag